This invention relates to high pressure sodium lamps and more particularly to such lamps having an arc tube of reduced size, lower cost and greater efficiency.
Additionally, these lamps operate at high temperature and with reduced mercury thus allowing these lamps to pass the Toxicity Characteristic Leaching Procedure (TCLP).
High pressure sodium (HPS) lamps are in wide use worldwide because of their high efficacy, long life and acceptable color rendering properties. The acceptable commercial development of these lamps is generally attributed to the creation of arc tubes of translucent polycrystalline alumina (PCA), this being the first material that could be manufactured economically that would provide acceptable optical properties and yet withstand the attack of the sodium vapor.
Recently, improved versions of PCA have been developed that, under proper conditions, will allow operation of HPS lamps at high temperatures. These materials are disclosed in U.S. Pat. Nos. 4,285,732; 5,625,256; and 5,682,082.
It would be an advance in the art if HPS lamps could be developed that used these materials to provide increased efficacy and reduced cost. Further, it would be a definite advance in the art if such lamps could be built which would reduce pollution by passing the government instituted Toxicity Characteristics Leaching Procedure (TCLP) allowing conventional disposal in land-fills.
It is, therefore, an object of this invention to obviate the disadvantages of the prior art.
It is another object of the invention to enhance HPS lamps.
Yet another object of the invention is the reduction in cost of providing such HPS lamps.
Still another object of the invention is an increase in efficacy of HPS lamps together with a reduction in the amount of mercury employed.
These objects are accomplished, in one aspect of the invention, by a high pressure sodium lamp having an evacuated glass envelope with a plurality of electrically conductive support members therein and extending therethrough. An elongated arc tube having a pair of electrodes extending therethrough is affixed to the electrically conductive support members within the glass envelope. A gas fill includes a quantity of mercury and sodium within the elongated arc tube. The arc tube is selected from a translucent material that, when the lamp is operating, will have a wall temperature of about 1250xc2x0 C., a wall loading of from about 18.9 to about 22.2 w/cm2, and a power consumption of from 150 to 400 watts.
Further, the amount of mercury is reduced from 14.4 mgs/arc tube to 10.8 mgs/arc tube, allowing lamps having power consumption""s from 150 to 400 watts to pass TCLP.